(1) Field of the Invention
The present invention relates to a resin intake manifold, and more particularly to a resin intake manifold which is arranged between a cylinder head of an engine and a throttle body.
(2) Description of the Prior Art
(i) Prior Art Relevant to First Aspect of the Present Invention
In conventional, as a resin intake manifold, there has been known a structure in which a resonator serving as a resonant chamber is independently provided in a dead space within a surge tank, for the purpose of effectively utilizing the dead space (refer to, for example, Japanese Unexamined Patent Publication No. 11-229981).
However, in accordance with the prior art mentioned above, since the resonant chamber is formed by using a flat member, there is a problem that in the case that a great positive pressure is rapidly applied to an inner side of the surge tank due to a back fire or the like, a stress is concentrated and a strength is lowered.
(ii) Prior Art Relevant to Second Aspect of the Present Invention
As is well known, the intake manifold is arranged between the throttle body and the cylinder head of the engine, and is structured such as to have a function of evenly distributing the air fed from a side of the throttle body into a plurality of cylinders in a cylinder head of the engine. The intake manifold is formed by an aluminum material or a resin material for the purpose of weight saving, and is constituted by a surge tank reserving the air fed from the side of the throttle body, and a plurality of branch pipes distributing the air reserved in the surge tank into the respective cylinders. Each of the branch pipes is structured such that one end has a suction port and is connected to the surge tank, another end has a discharge port and is connected to the cylinder head of the engine, and an air passage is formed between the suction port and the discharge port.
In recent years, since a cost reduction and a complex shape are required, the intake manifold is frequently formed by the resin material. The resin intake manifold is formed so as to be separated into two pieces or three pieces, and the separated portions are generally bonded in accordance with a vibration welding so as to be integrally formed.
The vibration welding is carried out by overlapping a pair of welding flange portions formed in the separated portions so as to pressure weld by using a jig, and thereafter transversely vibrating the jig in a direction orthogonal to a pressure welding direction so as to weld the welding flange portion on the basis of a friction heat. The welding flange portion is formed so as to protrude to an outer side from a wall portion of the surge tank, and the intake manifold is formed by bonding the protruding portions to each other.
At this time, a stress is applied to the bonded portion obtained by the vibration welding by the rapid positive pressure applied to the inner portion of the surge tank due to a miss fire of the engine or the like. When the stress becomes greater, the bonded portion tends to be broken. Accordingly, there can be considered that a pressure resisting shape is formed by increasing a thickness of a wall portion in the surge tank, however, since a weight is increased at a degree that the thickness is increased, this structure is not preferable.
Further, in the case that the thickness of the wall portion in the surge tank is increased, since thickening a side of an inner wall portion of the wall portion reduces a capacity of the surge tank, this structure is not preferable. Further, since thickening a side of an outer wall portion of the wall portion inversely makes the protruding portion of the welding flange portion narrow so as to make a pressure welding area of the jig small, the welding force is reduced, and a welding efficiency is lowered.
(iii) Prior Art Relevant to Third Aspect of the Present Invention
Nowadays, in view of the weight saving or the like, a resin intake manifold injection molded by a synthetic resin is going to be put on the market.
Accordingly, there is a resin intake manifold provided with a surge tank portion, an even number of intake pipes branched from the surge tank portion and connected to respective cylinders, and mounting flange portions formed in leading end portions of the intake pipes and connected to a cylinder head (refer to, for example, Japanese Unexamined Patent Publication No. 2000-179419).
Further, the resin intake manifold is mounted to the cylinder head via the mounting head at a connecting position provided on a diagonal line in the periphery of each of the cylinders, as described in Japanese Unexamined Patent Publication No. 2000-179419. In other words, for example, in the case of four cylinders, the connecting position appears in a zigzag shape, that is, near side→far side→near side→far side.
Further, in general, in a state in which each of bolt holes formed in the mounting flange is inserted through by a stud bolt protruding from a seat surface of the cylinder head and arranged in a zigzag shape, the mounting flange and the seat surface of the cylinder head are connected by fastening a nut.
At a time of the fastening work of the nut, there is a risk that the bolt drops from a gap formed between the intake pipes. In particular, in the case of mounting at the far side position, a mounting workability is not good, and there is a risk that the bolt drops during the mounting work.
In the case that the intake manifold is formed by a resin material with high water absorbability such as a polyamide 6 or the like, there is a risk that the intake manifold hygroscopic swells. Further, in the case of being in contact with a snow melting agent (a calcium chloride solution) for a long time, there is a risk that a stress crack caused by a metal salt is generated.